1. Field of the Invention
This invention pertains to an improved splice means, and further relates to a flexible abrasive belt having free ends joined with the splice means.
2. Background Art
Numerous sheet-like or layered articles which employ a backing layer of a tough flexible material are known. Typical examples include abrasive sheets, such as coated abrasive articles, pressure-sensitive adhesive tapes, photographic film, magnetic recording tape, and so forth. Of these, for example, a coated abrasive article comprises a flexible backing material having a plurality of abrasive particles adhered on one major surface thereof. The backings employed typically include paper, film forming plastic, cloth, metal foil, and the like.
These sheet-like materials, such as abrasive sheets, are typically formed or presented in a discrete nonendless form. As a consequence, the free ends of the sheet material(s) must be joined or spliced if it is desired to either lengthen a strip by joining a plurality of separate sheets, or, alternatively, if it is desired to form an endless belt arrangement from a single discrete sheet. However, there can be difficulties in successfully splicing free ends of sheet material, especially where the finished spliced article is destined for rigorous treatment in service.
For instance, flexible abrasive articles are available in a wide variety of forms such as endless abrasive belts, tubes, sleeves, discs and discrete sheets. A very popular form of flexible abrasive article is an endless belt that is fabricated by joining two free ends of the abrasive material together to form a joint, also known as the splice. In some constructions, the splice is held together by a splice adhesive applied to each of the two free ends and a splice media or means overlying the line of juncture and bonded to the splice adhesive.
These endless abrasive belts are often subjected to rigorous grinding conditions involving high temperatures, such as 200.degree. C., and high grinding pressures, such as 10 kg/cm.sup.2. The splice must be able to withstand these conditions so that the abrasive belt remains intact under such severe grinding conditions. Thus the splice adhesive and splice media each must be sufficiently heat resistant and tough to prevent a failure from occuring at the splice site before it happens in other areas of the abrasive article under severe grinding conditions. Naturally, good adhesion is desired between the splice adhesive and splice media. If either the splice adhesive or splice media cannot withstand such severe conditions, the splice will break or rupture. This breakage will end the useful life of the abrasive belt and full utilization of the abrasive belt is not achieved.
In addition to providing high adhesion within its own structural elements and with the free ends of the abrasive article, the splice media, as incorporated into the coated abrasive article, also must show good backwear properties. During use, the backside of the coated abrasive belt traverses over two or more idler wheels or contact wheels. As the splice media typically is located over the juncture or joint area on the backside of the abrasive article, tremendous wearing action is exerted on the splice media. Thus the splice media also must possess excellent wear resistance properties to avoid wear breakage.
It can be understood that what is desired by the abrasives industry is a splice that will consistently withstand relatively high temperatures and relatively high grinding pressures, as well as provide relatively high resistance to backwear throughout the entire useful life of the flexible abrasive article. Numerous proposals have attempted to address this need, although not thought to provide resolution without raising their own peculiar problems.
For instance, U.S. Pat. No. 2,733,181 (Riedesel) pertains to a coated abrasive splice media that comprises natural or artificial fibers or filaments such as glass or nylon filaments. The fibers or filaments typically are embedded into a thermoplastic or thermosetting adhesive. However, the thermosetting adhesives exemplified by Riedesel are solvent based, which requires increased cost and labor input as special precautions must be provided for the handling, ventilation and removal of the solvent and solvent emissions. On the other hand, Riedesel states that thermoplastic adhesives in the splice media ordinarily are ineffective for use with abrasive belts which heat up during operation.
U.S. Pat. No. 4,215,516 (Huschle et al.) teaches a splice media containing unidirectionally-oriented organic fibers such as polyamide or polyester type fibers. The fibers are embedded in an adhesive, which is variously exemplified as solvent based systems of a mixture of linear saturated esters of sebacic and terephthalic acids esterified and ethylene glycol modified with a cross linking agent such as polymethylene polyphenyl isocyanate; as well as an imide-amide-polyester copolymer, or polyurethane resin. Again, a solvent based splice media adhesive is undesirable as it requires increased cost and labor input attendant to the special precautions needed for handling and removal of the solvent and solvent emissions. Further, the adhesive solvents described by Huschle et al. for forming the solvent systems are chlorocarbons, such as methylene chloride and 1,1,2-trichloroethane, which are obsolescent materials.
U.S. Pat. Nos. 4,011,358 and 4,091,150 (Roelofs) teach a splice media comprising a coextruded multilayer polyester film comprised of two monolithic layers having no fiber reinforcement, and a splice formed with such a splice media. The first layer is a noncrystalline adhesion-promoting layer which imparts toughness to the splice media and provides good adhesion with the splice adhesive. The second layer is a highly crystalline base layer which imparts strength to the splice media. Roelofs discloses, in the background section, mechanical roughening of the surfaces of polyester film to increase the adhesion to an adhesive.
U.S. Pat. No. 4,027,435 (Malloy) discloses a partially cured heat-activatable adhesive film as a preformed splice film used for splicing a coated abrasive article into an endless belt. The splice film adhesive can be used in a lap or butt splice arrangement between juxtaposed free ends of an abrasive sheet. While Malloy purports that no solvent from the splice adhesive film is evaporated in the belt making area; yet, the incipient preparation of the adhesive film does nonetheless involve handling of solvent based adhesive components. Also, while Malloy discloses an optional separate woven backing for the adhesive film which would be distanced from the splice site, there is only disclosed a monolithic adhesive film and no mention is made of reinforcing the splice adhesive layer itself with constituent fibers.
U.S. Pat. No. 4,082,521 (McGarvey) discloses a laminated patch splice for an endless coated abrasive belt. The patch splice is described as a slit woven fabric laminated to a plastic film, and the woven fabric is placed over the splice adhesive used to join the patch and free ends of an abrasive article. McGarvey teaches that preferred plastic films include polyimide, polyester, polyethylene, and cellulose triacetate film. On the other hand, the woven fabric is consolidated with the plastic backing film by fusion or an extraneous adhesive, such as polyurethane adhesives, epoxy adhesives and nylon-phenolic adhesives. The polyurethane adhesives can be thermoplastic or thermosetting. However, the axial fibers in the woven fabric layer of the patch splice in McGarvey are arranged as nonaligned and nonparallel with the running direction of the spliced endless belt, which typically is the direction of greatest stress developement in the belt. As the industry improves the strength of the abrasive side of the coated abrasive article, the splice must also be improved so that the splice does not become a source of structural failure in the coated abrasive article.
The field still awaits an improved splice means for abrasive articles which possesses strong internal cohesion and wear resistance and displays good adherability to a splice adhesive, while reducing the need for added adhesive steps and handling of bothersome and noxious adhesive solvents.